This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A215152 #23 Jan 16 2025 02:38:24
%S A215152 0,0,0,21,445,5457,55576,527138,4824694,43484124,389855718
%N A215152 Number of sphenic triples up to 10^n.
%C A215152 The sphenic triples {1309, 1310, 1311}, {1885, 1886, 1887}, ... are counted once at a time.
%o A215152 (PARI) issemiprime(n) = factor(n)[,2]~ == [1,1];
%o A215152 issphenic(n) = factor(n)[,2]~ == [1,1,1];
%o A215152 list(nmax) = {my(c = 0, pow = 10, lim = 10^nmax/2+1); forstep(k = 1, lim, 2, if(issemiprime(k) && issphenic(2*k-1) && issphenic(2*k+1), c++); if(2*k-1 > pow, print1(c, ", "); pow *= 10));} \\ _Amiram Eldar_, Jan 15 2025
%Y A215152 Cf. A007304, A215217, A066509, A215218, A215015.
%K A215152 nonn,more
%O A215152 1,4
%A A215152 _Martin Renner_, Aug 06 2012
%E A215152 a(8)-a(10) from _Bert Dobbelaere_, Jul 15 2023
%E A215152 a(11) from _Amiram Eldar_, Jan 15 2025